Abstract-This paper presents an overview of the current activity at the Technical University of Denmark in the field of ultra-wideband monolitic microwave integrated circuits (MMICs) for next-generation high-resolution synthetic aperature radar (SAR) systems. The transfer function requirements for MMIC components in a wideband SAR systems are described. The design and performance of a DC-to-X-band SiGe HBT quadrature mixer and a C-band GaAs pHEMT downconverter are described. Experimental results demonstrates the usefulness of the designs for quadrature modulation/demodulation and downconversion of ultra-wideband linear FM-modulated signals.